1. Field of the Invention
The present invention relates to a pellicle that prevents a particle from directly lying on a mask used for exposing a wafer, to thereby defocus the particle.
2. Description of the Related Art
Pellicles have been widely used in semiconductor manufacturing in order to reduce the influence of foreign particles when exposing wafers using a mask.
FIG. 1 shows a structure of a conventional pellicle. The pellicle principally incorporates a pellicle frame 20 and a pellicle membrane 30. A typical pellicle membrane 30 may include, for example, nitrocellulose and fluoropolymers. Because the pellicle membrane 30 has a thickness of approximate 1 micron it has very little strength to resist external forces. In addition to the pellicle frame 20 and the pellicle membrane 30, the pellicle incorporates a first adhesive 40 and a second adhesive 50. The pellicle frame 20 supports the pellicle membrane 30, wherein they are adhered to each other by the second adhesive 50. In the process of manufacturing semiconductors, a mask 10 is first prepared. The mask 10 is then cleaned and thereafter the surface of the mask 10 is inspected to detect any particles lying on the mask 10. After it has been confirmed that the surface satisfies given criteria, the pellicle is mounted onto the mask 10. Thereafter, the surface of the mask 10 is checked again. When the mask 10 is in good condition, a light source (not shown) placed at a side of the mask 10 irradiates a ray toward the mask 10, whereby a wafer (not shown) placed at another side thereof is exposed to the ray through the mask 10.
In mounting the pellicle onto the mask 10, the pellicle is pressed to the mask 10 using the pellicle mounting system 60. This pressing and the first adhesive 40 enables the pellicle to be fixed on the mask 10. The first adhesive 40 may preferably be covered with a liner (not shown) for ease of handling. Such a liner is then removed before the pellicle is mounted.
As shown in FIG. 1, pressure is applied with the contact of the pellicle membrane 30 and the pellicle mounting system 60. In other words, the pellicle mounting system 60 directly presses the pellicle membrane 30. Because the pellicle membrane 30 is thin and therefore weak to external force, this pressing may damage the pellicle membrane 30. Such damage, if severe, might cause foreign particles to invade the space surrounded by the mask 10 and the pellicle. Alternatively, the pellicle membrane 30 may peel away from the pellicle frame 20.
To detect a particle on the mask 10, a method is used wherein a light source obliquely irradiates a ray toward the mask 10 and a light detector detects a ray scattered by the particle. However, a conventional pellicle frame 20 might block a ray scattered by a particle lying near the pellicle frame 20 from reaching the detector, thereby blocking detection of such a particle.
Related to this, the size of such pellicle membranes 30 has increased and as a result, there are instances where the pellicle membrane 30 bends to its own weight. As a result, the exposure of the wafer fails, that is, the pattern on the mask 10 cannot be accurately copied to the wafer.